Electrostatic painting of substrates is desirable because it can reduce paint waste and solvent emissions as compared to non-electrostatic painting techniques. Electrostatic painting techniques, however, require the substrate to be electrically conducting. If the material is itself not electrically conducting, to provide increased paint transfer efficiency during electrostatic painting, the material is required to be made conducting. This can be done by using an applied prepcoat which is electrically conducting. In the past, injection molded articles made from electrically insulating thermoplastic materials like XENOY.TM. or thermoplastic olefin (TPO), used such an applied conducting primer to improve electrostatic painting. Applying such prepcoats increases manufacturing complexity.
The invention of U.S. Pat. No. 5,484,838 improves on such surface conductivity imparting methods by disclosing a thermoplastic polymer blend which had increased electrical conductivity throughout the bulk of the substrate bulk material. This bulk conductivity was provided by the addition of electrically conductive carbon black to the polymer blend. In particular, the blend comprises at least a crystalline polymer and an amorphous or semi-crystalline polymer wherein at least a portion of the carbon black is dispersed within the crystalline polymer. Such electrically modified bulk material, particularly TPO, is used in the automotive industry in a variety of molded articles including bumper fascias, instrument panels, and mirror housings painted by electrostatic methods. Since carbon is black, it imparts a black color to the final product. An adhesion promoting layer is generally applied to this carbon black modified TPO before application of a basecoat and clearcoat in order to improve adhesion to the TPO.
It is an object of this invention to provide a plastic material useful in automotive applications which can be partially painted electrostatically while being colored other than black. That is, to be able to be colored to match or compliment the color of an automotive vehicle. It is another object of the present invention to provide a plastic material which may be painted without an applied primer coat to improve adhesion between of the paint and the TPO substrate. The present invention meets these objects as will be explained in detail.